The overtube is employed for safely and smoothly inserting and removing an endoscope into and from a body cavity (for example, refer to a patent document 1). Normally, an anti-leak valve is attached to a base end portion of the overtube, in order to prevent leakage of air supplied into the body cavity.
Generally, the anti-leak valve used with the overtube is made of a rubber or silicone rubber that can follow up the movement of the endoscope, and fixed to a portion of the overtube or to a grip (for example, refer to a patent document 2).
In the event of executing Endoscopic Mucosal Resection (EMR) which is an operation of endoscopically resecting a mucous membrane of esophagus, stomach, or colon, conventionally a snare is employed for dividing the diseased tissue in the case where the diseased part is large, and since the diseased tissue that has been resected is relatively small, the structure and shape of the endoscope insertion port of the conventional anti-leak valve allows taking out the diseased tissue without damage.
Recently, Endoscopic Submucosal Dissection (ESD), which is an operation of endoscopically dissecting a submucosa of esophagus, stomach, or colon, has rapidly come to be widely adopted. The ESD is generally executed with the endoscope inserted through the inner cavity of the overtube inserted into the body cavity. Then a high-frequency treatment device is made to stick out from the distal end through the forceps channel of the endoscope, and manipulated while moving the endoscope back and forth, up and down, or rotationally with respect to the overtube. Accordingly, a gap is prone to be formed between the valve element of the anti-leak valve attached to the base end portion of the overtube and a proximal end portion of the endoscope. The formation of the gap between the valve element of the anti-leak valve and the endoscope incurs the problem that the air supplied into the body cavity leaks through the gap and the body cavity is thereby deflated, which degrades the visual field of the endoscope. Also, in the case where the air supply to the part to be treated is insufficient, the part cannot be sufficiently inflated, which may make it difficult for the operator to execute the procedure.
Further, in the case of ESD the diseased part is often collectively resected, and hence the diseased part to be extracted is generally larger than in the case of EMR. However, since the endoscope insertion port of the anti-leak valve is relatively small, the extraction of the diseased part with the anti-leak valve attached to the overtube is technically difficult, especially in the case of ESD. More particularly, because of the presence of the anti-leak valve attached to the base end portion of the overtube, the diseased tissue is damaged when the endoscope passes through the anti-leak valve, or the extraction of the entirety of the diseased tissue is disabled.
[Patent document 1] JP-A No. 2005-046273
[Patent document 2] JP-U No. 3129543